Gallium arsenide diode with up-converting phosphor coating

ABSTRACT

Adjustable color in the visible spectrum results from use of a gallium arsenide infrared emitting diode provided with a coating of a composition having at least one each of two different anions in some unit cells. The composition exemplified by a variety of oxyhalides contain the cation pair Yb3 -Er3 , Yb3 -Ho3 and mixtures thereof.

[72] inventors Shobha Singh Summit; LeGrand G. Van Uitert, MorrisTownship, both 0! NJ.

[21] Appl. No. 816,764

[22] Fiied Apr. 16, 1969 [45] Patented Nov. 16, 1971 [73] Assignee BellTelephone Laboratorim Incorporated Murray Hiii, NJ.

[5 GALLIUM ARSENIDE DIODE WITH UP- CONVERTING PHOSPHOR COATING PrimaryExaminer-Robert Sega! Attorneys-R. .l. Guenther and Edwin B. CaveABSTRACT: Adjustable color in the visible spectrum results 9cmmsznmwmgFigs from use of a gallium arsenide infrared emitting diode pro- [52]U.S. Cl 313/1G8D, vided with a coating of a composition having at leastone each 307/883, 331/94.5,252/3-01.4 of two different anions in someunit cells. The composition ex- [51] Int. H01) 1/62, amplified by avariety of oxyhalides contain the cation pair H0 1 j 63/04, H015 3/00Yb-Er, Yb-Ho*and mixtures thereof.

25000 ti E 55 520000 2 g 315000 E 21349 Ia 313/501 t: 1' a 1.

PATENTEUHUV 1s IQTl 3.621.340

EQERGY LEVEL- WAVE NUMBERS (C M") 8 /Nl/EN7 0R$ 5 S-S/NGH LG. VAN U/TERTA T TORNE V GALLXUM ARSENIDE DIODE WITH UP-CONVERTING PHOSPHOR COATINGBACKGROUND OF THE INVENTION 1. Field of the Invention The invention isconcerned with electroluminescent devices having outputs at visiblewavelengths and with phosphors used in such devices. contemplated use isin display devices on communication and computer equipment.

2. Description of the Prior Art A variety of low power level,electroluminescent devices have been described. A common class utilizesa forwardbiased PN junction semiconductor diode.

The best publicized PN junction electroluminescent devices utilizegallium phosphide. Depending on which of the popular dopants, oxygen ornitrogen, is used, these diodes may emit at red or green wavelengths.

A recently announced class of devices depends on the use of an up-conerting phosphor coating on a gallium arsenide junction diode. This wasrecently described in an article by S. V. Galginaitis, et al.International Conference on GaAs, Dallas, Oct. l7, I968, SpontaneousEmission Paper No. 2. The device depends on a phosphor coating whichdepends upon the presence of ytterbium acting as a sensitizer and erbiumacting as an activator. Conversion from the infrared output of the GaAsjunction to a green wavelength is brought about by a sequential (orsecond photon) process.

Gal devices containing both types of doping may simultaneously emit atgreen and red wavelengths. Since the red emission eventually saturateswith increasing power while the green does not, the possibility ofvarying apparent color output by varying input power is implicit. Since,however, red emission is also significantly more efficient, thelikelihood of producing a dominant green output is small. Little if anyattention has been directed to such an adjustable color GaP device inthe literature.

Coated GaAs devices described in the literature have invariably operatedwith output in the green.

SUMMARY OF THE INVENTION GaAs infrared diodes are provided with phosphorcoatings of a class of compositions, including compounds, in which atleast two available anion sites in some unit cells are differentlypopulated and which manifest adjustable visible color output. Compoundsare exemplified by various oxyhalide stoichiometries in which the halideto oxygen ratio equals or exceeds unity. As in known coated GaAs diodes,up conversion results from inclusion of trivalent ytterbium which servesas a sensitizer. This sensitizer ion is invariably paired with anactivator which may be trivalent erbium or trivalent holmium. Undercertain circumstances, advantages such as color adjustability and colorequalization may result from physically mixed compounds containingdifferent activators.

The unmodified oxychloride compound having a l:l chlorine to oxygenratio and containing the single pair, Yb- Er, is not a preferredcomposition for these purposes, since output is predominantly red underusual input conditions. However, modifications may result in enhancementof color adjustanility. One such modification takes the form of a simpleincrease in the chlorine to oxygen ratio, another takes the form ofdilution of the 1:1 compound with a diluent such as PbFCl or NaYF,Cl,, athird includes a mixture of or and Ho activators in the same compositionand a fourth includes a mixture of compounds, one of which at least maycontain Ho. Preferred embodiments of the invention are so described.

Certain of the phosphor compositions herein are novel and so representadditional embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a front elevational view ofan infrared emitting diode having a phosphor converting coating inaccordance with the invention; and

FIG. 2 is an energy level diagram in ordinate units of wave numbers forthe ions Yb, Er and Ho within the crystallographic environment providedby a composition herein.

DETAILED DESCRIPTION 1. Drawing Referring again to FIG. I, galliumarsenide diode 1 containing PN junction 2, defined by P and N regions 3and 4, respectively, is forward biased by planar anode 5 and ringcathode 6 connected to power supply not shown. Infrared radiation isproduced by junction 2 under forward biased conditions, and some of thisradiation, represented by arrows 7, passes into and through layer 8 of aphosphorescent material in accordance with the invention. Under theseconditions, some part of radiation 7 is absorbed within layer 8, and amajor portion of that absorbed participates in a two-photon or higherorder photon process to produce radiation at a visible wavelength/s. Theportion of this reradiation which escapes is represented by arrows 9.

Potentiometer 10, in series with diode 1, serves the function ofpermitting adjustment of input power to the diode thereby varying theinfrared emission and, in consequence, altering the apparent colorouqiut of emission 9 in accordance with the invention. This element isintended to be illustrative of variable power input means which may beoperated to adjust or alter apparent output frequency on occasion, in acontinuous fashion or in any other desired manner.

The main advantage of the defined phosphors is best described in termsof the energy level diagram of FIG. 2. While this energy level diagramis a valuable aid in the description of the invention, two reservationsmust be made. The specific level values, while reasonably illustrativeof those for the various included compositions of the noted type, aremost closely representative of the oxychloride systems either of theYOCl or Y OChstoichiometries. Also, while the detailed energy leveldescription was determined on the basis of carefully conductedabsorption and emission studies, some of the information contained inthe figure represents only one tentative conclusion. In particular, theexcitation routes for the 3 and 4 photon processes are not certainalthough it is clear that certain of the observed emission represents amultiple photon process in excess of doubling. The diagram is sufiicientfor its purpose; that is, it does describe the common advantage of theincluded host materials and, more generally, of the included phosphorsin the terminology which is in use by quantum physicists.

FIG. 2 contains information on Yb", Er and Ho. The ordinate units are inwavelengths per centimeter (cm."). These units may be converted towavelengths in angstrom units (A) or microns (n) in accordance with therelationship:

Wavelength= The left-hand portion of the diagram is concerned with therelevant manifolds of Yb in a host of the invention. Absorption in Ybresults in an energy increase from the ground manifold Yb'-'F-,,, to theYb F manifold. This absorption defines a band which includes levels atl0,200 cmf l0,500 cmf'" and 10,700 cmf The positions of these levels areafi'ccted by the crystal field splitting within the structures having atleast one each of two different anions or at least one anion vacancy perunit cell or formula unit. In the oxychlorides, for example, theyinclude a broad absorption which peaks at about 0.935;; l0,7OO cm.'""),there is an efficient transfer of energy from a silicon-doped GaAs diode(with its emission peak at about 0.93,u.). This contrast with thecomparatively small splitting and weaker absorption at 0.93 p. inlanthanum fluoride and other less anisotropic hosts in which absorptionpeaking is at about 0.98 it for Yb.

The remainder of FIG. 2 is discussed in conjunction with the postulatedexcitation mechanism. All energy level values and all relaxationsindicated on the figure have been experimentally verified.

2. Postulated Excitation Mechanisms Following absorption by Yb, ofemission from the GaAs diode, a quantum is yielded to the emitting ionEr (or as also discussed in conjunction with the figure, to Ho). Thefirst transition is denoted 11. Excitation of Er to the 1, is almostexactly matched in energy (denoted by m) to the relaxation transition ofYb. However, a similar transfer, resulting in excitation of Ho to Holrequires a simultaneous release of one or more phonons (+P). Themanifold Erl has a substantiai lifetime, and transfer ofa second quantumfrom Yb promotes transition 12 to the ErF manifold. Transfer of a secondquantum to Ho results in excitation to H 8, with simultaneous generationof a phonon. lntemal relaxation is represented on this figure by thewavy arrow 1 ln erbium, the second photon level (Er-"F,,,) has alifetime which is very short due to the presence of close, lower lyinglevels which results in rapid degradation to the ErS state through thegeneration of phonons.

The first significant emission of Er is from the ErS state (18,200cm.'"" or 0.55p. in the green). This emission is denoted in the figureby the broad (double line) arrow A. The reverse of the second photonexcitation, the nonradiative transfer ofa quantum from ErF back to Ybmust compete with the rapid phonon relaxation to ErS and is notlimiting. The phonon relaxation to El i also competes with emission Aand contributes to emission from that level. The extent to which thisfurther relaxation is significant is composition dependent. The overallconsiderations as to the relationship between the predominant emissionsand composition are discussed under the heading Composition."

Green emission A at a wavelength of about 0.55u corresponds to thatwhich has been observed for or in LaF In accordance with this invention,it has been shown that the structures having mixed anions or anionvacancies with large resulting anisotropic environments about thecations are characterized by large crystal field splitting and improvedabsorption of GaAszSi emission by Yb. Large crystal field anisotropicsalso result in increased opportunity for internal relaxat on mechanismsinvolving phonon generation which thus far have not been found to bepronounced in comparable but more isotropic media. For Er, this enhancesemission B at red wavelengths. Erbium emission B is, in part, broughtabout by transfer of a third quantum from Yb to or 3* which excitesSince the phosphors of the invention are in powder or polycrystallineform, growth presents no particular probiem.

the ion from Ens to ErG with simultaneous generation of a phonon(transition 13). This is followed by internal relaxation to ErG which,in turn, permits relaxation to ErF by transfer of a quantum back to Ybwith the simultaneous generation of a phonon (transition 13). The EFF,levei is thereby populated by at least two distinct mechanisms andindeed experimental confirmation arises from the finding that emission Bis dependent on a power of the input intensity which is intermediate incharacter to that characteristic of a three-phonon process and thatcharacteristic ofa two-phonon process for the Y OCl, host. Emission B,in the red, is at about 15,250 cmf or 066p.

While emissions in the green and red are predominant, there are manyother emission wavelengths of which the next strongest designated C isin the blue (24,400 cm. or 0.4m). This third emission designated Coriginates from the Er=l l level which is, in turn, populated by twomechanisms. in the first of these, energy, is received by a phononprocess from ErG The other mechanism is a four-photon process inaccordance with which a fourth quanta is transferred from Yb to Erexciting ErG from ErG (transition 14). This step is followed by internalrelaxation to Er D from which level energy can be transferred back to Ybrelaxing or to Er=i-l,,, (transition 14).

Significant emission from holmium occurs only by a twophoton process.Emission is predominantly from H0 5, in the green (l8,350 cmf or0.54,u.). The responsible mechanisms are clear from FlG. 2 and theforegoing discussion.

3. Material Preparation Oxychlorides, for example, may be prepared bydissolving the oxides (rare earth and yttrium oxides) in hydrochloricacid, evaporating to form the hydrated chlorides, dehydrating, usuallynear [00 C. under vacuum, and treating with Cl; gas at an elevatedtemperature (about 900 C.). The resulting product can be the one or moreoxychlorides, the trichloride or mixtures of these depending on thedehydrating conditions, vacuum integrity and cooling conditions. Thetric'nloride melts at the elevated temperature and may act as a flux tocrystallize the oxychlorides. The YOCI structure is favored by high Ycontents, intermediate dehydration rates and slow cooling rates, whilemore complex chlorides such as (Y,Yb),OCl-, are favored by high rareearth content, slow dehydration and fast cooling. The trichlon'de maysubsequently be removed by washing with water. Dehydration should besufficiently slow (usually 5 minutes or more) to avoid excessive loss ofchlorine.

Oxybromides and oxyiodides may be prepared by similar means usinghydrobromic acid and gaseous HBr or hydroiodic acid and gaseous h! inplace of hydrochloric acid and Cl, in the process.

Mixed halides such as those containing both alkali metals and rareearths can be prepared by dissolving the oxide in HCl and precipitatingwith HF, dehydrating and melting the resulting material together near1,000 C. in vacuum. Lead or alkaline earth fluorochlorides andfiuorobromides may be prepared simply by melting the appropriate halidestogether. In both cases the products can, in turn, be melted togetherwith the oxyhalide phosphors to adjust their properties.

4. Composition a. Matrix The compositional requirements of the inventionhave been briefly set forth. Adjustability or tunability depend upon thecrystal field condit ons which have been observed in a number ofcompounds wherein the rare earth ion is in an anisotropic environment.Preferably, this anisotropy results by use of a host composition whichincludes at least one compound having a crystalline structure such thatthere are at least two available anion sites which are populateddifferently in at least 1 percent of the unit cells and preferably in atleast 5 percent of the unit cells. While this may take the form ol'acompound in which one such site is occupied while the other is not, themore usual form of the invention includes at least two different anionsin such unit cells. Examples of such compounds are: rare earth andyttrium, oxychlorides, oxybromides, oxyiodides, oxychall-togenides, e.g.those and mixtures of oxyhalides with fluorohalides, of the form M*M *X,and alkaline earth or lead fluorohalides of the form M x, where M Li,Na, K, Rb, C5 or Tl; M =Ca Sr, Ba or Pb; hi =Sc, La, Gd. Lu, Bi and X=F, cl. Br, or i. The l percent minimum requirement implies thepossibility of mixed host compositions and such mixtures may include anynumber of the foregoing.

The oxychlorides, oxybromides and oxyiodides are preferred; and, ofthese, the oxychloridcs are the most preferred class. These include atleast two different stoichiometries which may be designated inaccordance with their chlorine to oxygen ion ratios. The simpleststoichiometry exemplified by YOCl has the tetragonal D 7/4h P4/nmmstructure. A different stoichiometry has a hexagonal structure. Anexemplary material has a composition with the analyzed metal ratios:Y=56 percent, Yb=43 percent and Er=l percent, has lattice constants a=5.607, c =9.260 and has prominant d-spacings of 9.20, 2.33, 3.09, 4.62and 2.83. Analysis indicates the structure M OCl where M is one or moreof the cations of the rare earths and ytterbium.

For purposes of the discussion of this invention, oxychlorides arediscussed in terms of a tirst class in which the chlorine to oxygencation content is approximately equal to unity and a second class inwhich the chlorine to oxygen cation ratio is greater than unity. inaccordance with the said second class, a ratio of at least 1.5 isconsidered to suffice.

Such a minimal cation ratio requires at least the partial presence of anoxychloride phase other than that having a ratio of unity. For thepurposes of this invention, such minimal ratio constitutes a preferredembodiment since it is the only preferred compound class containing thesingle activator Er and which as otherwise unmodified may functionefficiently as an adjustable visible phosphor.

b. Sensitizer Content Every composition in accordance with thisinvention contains the cation pair Yb -Er although, as noted, this maybe modified as by addition, dilution or physical admixture. Yb is therequired sensitizer and it is to this ion that initial energy transferis first made from the infrared diode or other infrared source. Contentof this and other cations is discussed in terms of ion percent based ontotal cation content of the concerned compound. A minimum Yb content isset at 5 percent since appreciably less Yb is insufficient to result inreasonable conversion efl'iciency regardless of En content. A preferredminimum of about 10 percent on the same basis is based on an observedoutput intensity comparable to that of well engineered gallium phosphidediodes. These minimal applied universally to the total phosphorcompositions of the invention.

The maximum recommended Yb content is somewhat dependent upon the othernature of the phosphor composition.

To some extent, this fact is evident from the detailed descrip-' tion ofHO. 2. Regardless of the nature of the composition, a Yb content of 50percent is permitted in the absence of Ho additions. A contentapproaching 100 percent is permitted when H is present. The 50 percentcontent is not sufiiciently high to mask an otherwise obtainable greenemission by employing an adequate Er content and the presence of l--loassures green emission at iow power levels for any Yb content. Specificmaxima are discussed in terms of two systems. Oxyhalides containing X20ratios of at least 1.5

For compositions activated by Er alone the maximum Yb content is 50percent of the cations since beyond this level multiphoton processes inexcess of two photons become sufficiently efiicient under manyconditions to limit green emission. A preferred maximum lies at 40percent since essentially pure green remains attainable from Er for theusual range of content of this ion at some GaAs emission output level.However for compounds coactivated by at least l/O cation percent Ho theupper Yb limit approaches lOO percent (allowing only for activator).

Those including oxyhalide in which the X anion ratio is ap proximatelylzl These compounds emit red when sensitized by Yb and activated by Erfor all sensitizer concentrations. Therefore the upper limit for Ybapproaches 100 percent but these compositions suit the purpose of thisinvention only where modified. Modifications may be of any of threetypes. First, coactivation by adding limited amounts of Ho; second,dilutron with a flurohalide and third by physically mixing particulatebut distinct materials. in accordance with the first of these H0 isincorporated with Er' to the nominal extent of l0 percent of the latter.A dominant green emission is furnished by Ho at threshold infraredpumping levels from the diode while red emission from or is dominant athigh pumping levels.

The second modification takes the form of a dilution of 1:1 oxychloride,for exampie, by PbFCl or NaYF=Cl (where the compound is an oxybromide,it is expedient to diiute with NaYF r or PbFBr). Referring to the cationcontent of the mixed Yb -Er -cQntainmg compound, Yb may be permitted toapproach 80 percent beyond which the quality of the green obtainable isinsufficient for most purposes due to red contamination. A preferredmaximum lies at about 60 percent since substantial green purity isobtainable for feasible dilution ranges e.g. 40-90 mol percent PbFCl orequivalent).

in the third modification green emission is furnished by Ho which iscontained together with Yb within a crystal which may or may not containEr and red emission is furnished by Er contained together with Yb in asimilar matrix which does not contain an excessive amount of Ho.

. in general, the Ho content is about 10 percent of the Er content ormore for the first component and is less than lG percent and preferablyless than 3 percent of the Er content for the second. Since Ho emitspredominately in the green in every case and Er emits predominantly inthe red in these 111 oxyhalides the relative of the components may bechosen solely on the basis of the green purity which is required.Obviously the green-emitting component can be an Er activated materialthat fluoresces green such as Y Yb Er F NaY Yb F clor Na Yb Er ,WO,. Thecontent of sensitizer ('tb) in a given component may rise to levels of99+ percent. A physical mixture of this nature is considered useful forthese purposes where there is at least 5 mol percent ofthe dominantlygreen fluorescing compound.

c. Activator Content Er content is selected to maximize brightness forthis is the principal activator present, although other considerationsdictate limits. Generally, the erbium content is from about l/l6 toabout 20 percent. Below this minimum, brightness is not appreciable.Above the maximum, radiationless processes substantially q'uench output.A preferred range is from about V4 to about 2 percent. The minimum isdictated by the subjective criterion that only at this level does acoated diode with sufficient brightness for observation in a normallylighted room result. The upper limit results from the observation thatfurther increase does not substantidly increase output.

Holmium, recommended as an adjunct to erbium in conjunction withytterbium, may be included in an amount from about l/SO to about 5percent to enhance the green output of erbium. A similar result may beobtained by using mechanical mixtures of, for example, Yb -Er compoundand a Yb- Ho compound. The same limits apply to such admixtures with alllimits in ion percent of 10m! cations in the phosphor as above.

Where the required cation content of the host is not met by the totalYb-r-Er-r-Ho, diluent cations may be included to make up the deficiency.Such cations desirably have no absorption levels below any of the levelsrelevant to the described multiphoton processes. A cation which has beenfound suitable is yttrium. Others including Pb, Gd and Lu have been setforth above.

Other requirements are common to phosphor materials in general. Variousimpurities which may produce unwanted absorption or which may otherwisepoison" the inventive systems are to be avoided. As a general premise,maintaining the compositions at a purity level resulting from use ofstarting ingredients which are three nines pure (99.9 percent) isadequate. Further improvement, however, results from further increase inpurity at least to five nines level. For long term use many of theincluded compositions are desirably protected from certain environmentalconstituents. Glass, plastic, and other common incapsularits aresuitably used for such purpose.

The following examples are directed to a combination of a silicon-dopedGaAs diode with a phosphor or a combination of phosphors that appear toemit visible light that can be varied in color by changing the intensityof emission from the diode. The diode employed had a ZS-mil junction anda 72-mil dome. For 1.5 volts applied as a forward bias with a resulting2 amperes passing through the diode the output of the diode was 0.2watts at 093p. in each case the phosphor or combination of phosphors wasapplied directly to the diode dome as a =2 mil thick film usingcollodion as a binder. A constant voltage supply set for one volt wasused to supply current to the diode. The principal emissions affectingthe eye are red (at 066p.) and green (in the 0.54-0.55p. region). As theformer is the product of a three-photon process that drains the levelsresponsible for green emission in or and the latter is a two photonprocess for both or and Ho, the relative intensity of emission in thered increases rapidly with increasing diode emission (or increasingcurrent through the diode). To the eye, the apparent hue of the overallemission can thereby be varied from blue green through red including theintermediate shades.

EXAMPLE 1 Using a phosphor (Yb Er Y hOCl, the apparent emission wasgreen below 0.1 ampere, red above 0.5 ampere and changed in hue throughyellowish white in between.

EXAMPLE 2 Using the phosphor (Yb Er Ho Y OCl the apparent emission wasgreen below 0.2 ampere, red above 0.6 ampere and changed in hue inbetween.

EXAMPLE 3 Using a phosphor constituted as one-third Yb Er OCl by weightand two-thirds PbFCl by weight, a deep green emission was observed below0.3 ampere, red above 1.0 ampere and changing hues through yellow-whitein between.

EXAMPLE 4 Using a phosphor constituted as one-half Yb ,Er OCl by weightand one-half LiYFgclz by weight, a green emission was observed below 0.3ampere, red above 1.0 ampere and changing'hues through yellow white inbetween.

EXAMPLE 5 Using a mechanical mixture of (Yb Er Y Q OCl, and (Yb Ho )OClin a 240-1 weight ratio, the output appeared green below 0.2 ampere, redabove 0.8 ampere and changed in hue through yellow white in between.

The compositions listed below constitute additional examples ofmaterialscolorable under conditions similar to those of examples 1 through 5 oJMs QoUa a (Lu Yb Er hOCh oa osaas 'mm moonsln r Y oma moz moos oms amaoos ows o.oa ttous ot aus 'am ums o.s o.41s o.oz o.oos

os aus om ooos l vb ar pcm BaFCl Yb Er OCl-l SrFCl a Yb Er OCl'l CaFCl5a Yb Er oCl-l z LiLalQCl,

WEn oc-st NaLaF,Cl,

l Yb Er OCH KLaF cl 5: vs er oci-u NaGdF,Cl,

rs Yb Er OCl- /S CsGdF,Cl,

V4 Yb ,,,Er OCl-% LiBiF.

A Yb Er OCl'Va LiBiF Cl,

ii Yb Er OCl- NaBiF=Cl,

A: Yb Er OCl-A KBiBCl,

k vb ar ocus RbBiF,Cl,

A Yb Er oCl-li CsBiF C1,

V1 Yb Er Ho oCl' NaLaF Cl,

Yb Er l-lo ,OCl% TlLaF CI,

% osn om otom ya oJ oa 0.01 z z 56 vb er no pci-u TlGdF,Cl

particulate mixtures Yb Er oCl and 1a BaYb Er F,

% Yb Er Ol and 16 BaYb Er F The inventive concept is of immediate valuefor use in coated GaAs diodes along with such means as to provideadhesion, minimize scattering and protect from the environment and suchembodiment is preferred. Nevertheless, this is believed to be the firstphosphor system from which a variety of apparent visible colors may beexpediently produced by up conversion from infrared energy. It isapparent that such infrared energy may take other form. It may, forexample, be a coherent light source, such as a solid-state laser, andsuch source may be frequency or amplitude modulated by means of anancillary nonlinear element. This ancillary element may, for example, bea magneto-optic or an electro-optic modulator, a second harmonicgenerator; or it may be a parametric oscillator. Reasonably narrow bandinfrared energy may be produced by other means as from a monochrometerand broader band energy may also serve as a useful pump particularly byvirtue of the broad crystal splitting of the Yb absorption levels.

Since the inventive concept is dependent upon the apparent change incolor output of the phosphor, devices in accordance with the inventionnecessarily include means for changing the infrared power level incidenton the phosphor. While this generally takes the form of acurrent-varying or a voltagevarying element, such is not required.lnfrared power level may also be changed by means of filters, rotatingpolarizers, prisms and the like.

What is claimed is:

1. Device for producing emission in the visible spectrum consistingesentially of a phosphor composition comprising a crystallinecomposition containing the cation pair Yb -Er together with first meansfor illuminating said phosphor with infrared radiation within theabsorption spectrum for Yb characterized in that said composition has atleast two anion sites per unit cell which sites are differentlypopulated in at least 1 percent of the unit cells of said phosphor-inthat at least 5 cation percent of said phosphor is Yb and that thephosphor contains at least one cation in the minimum cation percentselected from the group which consists of 1/ 16 percent or and 1150percent H0 in which said composition is capable of converting saidinfrared radiation to visible emission by at least two energy processeseach producing a different emission wavelength, each of which invoves amultiphoton process which is at least a second-photon process, and inwhich second means is provided for varying the power level of said firstmeans to vary the intensity of the infrared radiation so as to alter therelative amounts of visible emission produced by the said two processes,and in which the phosphor consists essentially of a composition selectedfrom the group consisting of at least one compound seiected from thegroup approximately represented as consisting of oxyhalides in which thehalogen to oxygen ratio is greater than 1.5 and ROX mixed crystals andphysical mixtures;

the said mixed crystals being represented as consisting of 'ROX togetherwith at least one compound selected from the group consistingessentially of M RX and M *X the said physical mixture consistingessentially of a first component selected from the said compound, thecompound ROX, and the said mixed crystal, and a second componentconsisting essentially of a phosphorescent material which convertsinfrared radiation predominantly to visible radiation at a greenwavelength independent of powerlevel; in which M" is at least one of themonovalent ions of at least one element selected from the groupconsisting of Li, Na, K, Rb, Cs and T1, M is at least one of thedivalent ions of an element selected from the group consisting of Pb, CaSr, Ba, Cd, mg. and Zn, and in which the total R content is defined asconsisting of the trivalent ion of Yb in a minimum amount of 5 cationpercent of the total cations in the said phosphor composition and thetrivalent ion of or in a minimum amount of 1H6 cation percent of thetotal cations in the said phosphor cornposi tion and from 0 to 5 cationpercent on the same basis of the trivalent ion of Ho, but a minimum of1/16 cation pe cent He is included in the said compound ROX andremainder at least one diluent selected from the trivalent ions of theelements consisting of Bi, Y, Lu, Gd, Sc and La, and X is at least oneion of an element selected from the group consisting of F, Cl, Br and 1;said first means being a GaAs diode having said phosphor composition incontact therewith.

2. Device of claim 2 in which the diode is silicon doped.

3. Device of claim 1 in which the said minimum contents as set forth are10 percent Yb and l; percent or 4. Device ofclaim l in which the saidphosphor composition consists essentially of at least two differentcompounds each containing a cation grouping selected from the groupingsconsisting of Yb -Er" Yb"'-Ho, and Yb-Er"'-Ho 5. Device of claim 4 inwhich the phosphor consists essentially of an oxychloride with achlorine to oxygen ratio of at least 1.5.

6. Device of claim 5 in which both Er and ho are present.

7. Device of claim 4 in which the phosphor consists essentially of ROCiwith both Er' and Ho present.

8. Device of claim 4 in which the phosphor consists essentially ofROCltogether with M' PC].

9. Device of claim 4 in which the phosphor consists essentially of ROCltogether with M*RF,C1,.

i i i I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,621,340 Dated November 16. 1971 lnv -n fl Sbgbha, Si nghl LeGrand GrVanUj cert It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 6 1, "or" should read Er. Column 2,

I F. line 50, "(cm. T should read (om a lines 60 and 61, "cm. 7E shouldread "'1 n 7 n om and line 66, cm. should read cm i I Column 3, line 21,"cm. 7E should read om lines 33 and 1 x A l, "or" should read -Er--;lines 57 and 60, 'om. 7E should read -cm line 68, "or" should read Er-;and line 72,

1 "om. 7E should read om Column l, line t "those" should read -'.IHOS-.Column 5, line 22, 'minimal should read minima-; line 61, "or" shouldread --Er-; and line 71, before "ea." should be inserted Column 6, line12,

u a n n Yb should read Yb Er and lines 72 and 73, or

s n u should read Er Column 7, line 30, (Yb Ho 0Cl should read --(Yb HoY )OCl-. Column 8, line 17,

NaLa

"1/2. .l/2 should read --l/2. .1/2 NaLa. line 20, "l/2...l/2 should read1 2...l 2 LiGdF line 2 l 4 "l/2 should read l/2KY line 27, "g/uyb 979mb001.001 l/ L should read ---3/UYb Er Ho OCl'1/ lPbFCl--,' and line 36,1/2. .1/2Na 0.7. should read --l/2. l/2Na(Y Yb Column 9, line 10, "or"should read --Er-; and line 26,

"M x should read -M2+X2.- Column 10, lin 2, s" Should read -Mg--; andlines 6 and 19, "or should read Er.

Signed and sealed this 27th day of June 1 972.

'(SEAL) Attest:

EDWARD M.FLETCHER,J'R. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents RM P0-1050 (ID- USCOMM-DC BO376-P6Q U 5. GOVGRNMFNT PRINTINGOFIICE: IS! O-lfiO-JSI

2. Device of claim 2 in which the diode is silicon doped.
 3. Device ofclaim 1 in which the said minimum contents as set forth are 10 percentYb and 1/4 percent or
 4. Device of claim 1 in which the said phosphorcomposition consists essentially of at least two different compoundseach containing a cation grouping selected from the groupings consistingof Yb3 -Er3 , Yb3 -Ho3 , and Yb3 -Er3 -Ho3 .
 5. Device of claim 4 inwhich the phosphor consists essentially of an oxychloride with achlorine to oxygen ratio of at least 1.5.
 6. Device of claim 5 in whichboth Er3 and Ho3 are present.
 7. Device of claim 4 in which the phosphorconsists essentially of ROCl with both Er3 and Ho3 PRESENT.
 8. Device ofclaim 4 in which the phosphor consists essentially of ROCl together withM2 FCl.
 9. Device of claim 4 in which the phosphor consists essentiallyof ROCl together with M1 RF2Cl2.